Cellulose is an important constituent in plants and comprises anhydrous glucose units. Cellulose is utilized for making synthetic fibers for instance by spinning a yarn or a thread. Recycled cellulose can be regenerated and used for spinning yarn, thread, fibers etc.
There are several known ways to dissolve cellulose for various applications including manufacture regenerated cellulosic fiber. Often expensive chemicals are used in such processes. (Ohno H and Fukaya Y (2009) Task specific ionic liquids for cellulose technology Chemistry Letters V38)
Zhao et al, in Biotechnology and Bioengineering, pp. 1320-1328, Vol. 99, No. 6, 2008 discloses treatment of wood fiber bundles with NaOH and NaOH/Urea. There is disclosed treatment with cold NaOH. The treated pulp is neutralized. Any cellulose which is dissolved in the NaOH solution is apparently not used further. It is disclosed that treatment with cold NaOH is advantageous. The yield is improved with pretreatment.
WO 20101124944 discloses a process for the hydrolysis of cellulose comprising the sequential steps: a) mixing cellulose with a viscosity below 900 ml/g with an aqueous solution to obtain a liquid, wherein particles comprising cellulose in said liquid have a diameter of maximum 200 nm, wherein the temperature of the aqueous solution is below 35° C., and wherein the pH of the aqueous solution is above 12, b) subjecting the liquid to at least one of the steps: i) decreasing the pH of the liquid with at least 1 pH unit, ii) increasing the temperature by at least 20° C., and c) hydrolyzing the cellulose.
A. Isogai et al in Cellulose, vol 5, pp 309-319, 1998 discloses a method of dissolving cellulose in NaOH and then freezing the liquid.
A problem in the prior art is that when making a synthetic cellulose fiber from cellulose by for example a spinning process it may result in a mechanical weak fiber. This is particularly a problem when using recycled cellulose. Often the mechanical strength of the cellulose fiber is not satisfactory.
Another problem is that during some processes the pH value is changed for instance from high to low, which will add to the cost of the process.
Another problem when recycling cotton clothes is that some parts, which do not comprise cellulose, have to be removed. Examples include but are not limited to seams, buttons, fibers not based on cellulose and so forth.
There is a need for an improved process for regenerating cellulose, in particular when using recycled cellulose as a raw material for new cellulose fibers.